Dimmer circuits are used to control the power provided to a load such as a light or electric motor from a power source such as mains. Such circuits often use a technique referred to as phase controlled dimming. This allows power provided to the load to be controlled by varying the amount of time that a switch connecting the load to the power source is conducting during a given cycle.
For example, if voltage provided by the power source can be represented by a sine wave, then maximum power is provided to the load if the switch connecting the load to the power source is on at all times. In this way the, the total energy of the power source is transferred to the load. If the switch is turned off for a portion of each cycle (both positive and negative), then a proportional amount of the sine wave is effectively isolated from the load, thus reducing the average energy provided to the load. For example, if the switch is turned on and off half way through each cycle, then only half of the power will be transferred to the load. Because these types of circuits are often used with resistive loads and not inductive loads, the effect of repeatedly switching on and off power will not be noticeable as the resistive load has an inherent inertia to it. The overall effect will be, for example in the case of a light, a smooth dimming action resulting in the control of the luminosity of the light. This technique will be well understood by the person skilled in the art.
Such circuits usually consist of two parts, the first being a part to control the rate of rise of load voltage at each main half cycle. The second part is used to control the load current provided to the load via the use of a control switch. Various means are used to synchronise the action between these two parts, some more complex tan others. Traditionally, the synchronisation is achieved by a central control block which senses various parameters of the first part, determines when the second part should come into action and then upon such determination, provides control signals to the second part to control the switch. This circuit configuration is somewhat complex, both in design and implementation.
In devices that are mass produced, simplicity of design can lead to significant savings in cost during manufacture and an increased reliability in the function of the final product.
Similar considerations to each part of the circuit also apply and any simplification to any of the circuit blocks can lead to similar benefits.
Accordingly, it is an object of the present invention to provide a dimmer circuit arrangement which results in a simplified design.